Some conventional types of control system for an electric motor for use in a vehicle include an inverter circuit and a capacitor. The inverter circuit outputs an alternating current to an electric motor on the basis of an output voltage from a DC voltage source. The capacitor stabilizes the output voltage from the DC voltage source to the inverter circuit (for example, see Patent Literature 1).
In such a control system, a discharge start angle storage, in response to a request to discharge the capacitor, stores a present rotation angle of the rotor as a start angle θ0 before the start of discharge control by energization of the motor. A command current determining circuit determines command currents idr and iqr with which the torque of the motor is expected to be zero. A command current corrector performs rotation correction of the phases of the command currents idr and iqr by an angular difference Δθ between the start angle θ0 and the present rotation angle θ. Feedback control is performed on the current of the motor such that the command currents idr and iqr have the corrected phases. This controls the motor so that the motor is inhibited from generating a torque in response to the request to discharge the capacitor.